I got the sennheiser 250II which I've had enough of Beyer DT100's,
At the moment I’m using the desks headphone outputs (02R96) and a splitter, would I be doing the right move if I'll get the EAR HP4 amp and use it instead? Or is it a little too much luxury?

remember that a lot of true reference headphones are open-backed, and therefore offer no isolation. this may be a problem during tracking.

that said, the 650's are a great choice. i prefer, however, the grado rs-2's through the grado headphone amp. the grace headphone amp, however, is a very close second (analog side... the digital lacks the silk in the top end).

and, yes, if you're going to spend any amount of time under the cans (especially listening critically to a mix), you'll really notice how much of a difference the hp amp makes.

i rigged up an hpa-2 benchmark headphone amp
(just the card so i put it in a box wired it) and got some Akg k701's.

the akg's do need some serious burn-in time,
(there plugged into my stereo 24/7)
they were real bright at first but after 100 hours of burn-in they have rounded out a bit; some head-phone people say 300 hours before you really hear them.
I have some other headphones cheap sonys and akg 240 df .701's are in another league .
I'd like to try the hd 600 's as i know of a good mastering engineer who prefers them to the 650's fwiw.
I'd like to sell my 240df's toward some hd600 to try em out.
but the hpa -2 is great very clean and clear signal.
again some mastering folks i've read around here like this amp alot.

after 200 plus hours they are sounding very different then at first.
they are less strident in the high mids and tighter in bass.
they really do change alot!
they sound very good very detailed can't go back to by 240df's they sound kinds cardboardy which is wierd cause they use to seem revealing.....

remember that a lot of true reference headphones are open-backed, and therefore offer no isolation. this may be a problem during tracking.

that said, the 650's are a great choice. i prefer, however, the grado rs-2's through the grado headphone amp. the grace headphone amp, however, is a very close second (analog side... the digital lacks the silk in the top end).

and, yes, if you're going to spend any amount of time under the cans (especially listening critically to a mix), you'll really notice how much of a difference the hp amp makes.

--jon

To the original poster, if you're going to go with the 650's, a headphone amp will be essential. Neither the 650's or Grado will be good for tracking. The RS-1's from Grado are really incredible. I spent a lot of time A/Bing the Grado headphone amp with the headphones out on my Apogee Mini-Dac. Minimal difference (although this might have changed if I had a splitter in the path). If you go with Grado, you could start with the headphones for mixing and borrow a headphone amp to see if you notice a significant difference. Perhaps you could make do with a cheaper pair of closed for tracking.